Self-gush-cleaning filter device

ABSTRACT

A self-gush-cleaning filter device comprises a filter casing (1) provided with an inlet passage (a) and an outlet passage (d), a screen (11) disposed within the filter casing (1) so as to slide along the inner surface of the filter casing (1) in the flowing direction of a fluid, a foreign matter ejecting opening (15) being formed between the screen (11) and the inlet passage (a). A drive shaft (4) for driving the screen (11), a screen driving unit (3) for driving the drive shaft (4) so as to move the screen (11) quickly in a downstream direction in which the fluid flows from the inlet passage (a) toward the outlet passage (d) and to move the screen slowly in an upstream direction. An outlet shutoff valve (14) is disposed in the outlet passage (d) of the filter casing (1). The screen driving unit (3) is actuated after closing the outlet shutoff valve (14) to move the screen (11). When the screen (11) is moved quickly in the downstream direction, the fluid gushes from the downstream side through the screen (11) into the upstream side, and the foreign matters deposited on the screen (11) are removed from the screen (11) by the force of the gushing fluid.

TECHNICAL FIELD

The present invention relates to a filter device to be placed in a fluidinlet or a fluid conduit to remove dust and foreign matters contained ina fluid conducted through the fluid conduit. More particularly, thepresent invention relates to a self-gush-cleaning filter device providedwith a filter screen and having a function to remove rationally dust andforeign matters deposited on the filter screen.

In this specification, the term, "fluid" is used as a general termsignifying a liquid or a gas, and the term "foreign matters" is used asa general term signifying matters such as gravel, algae, slurries,grains or fragments of a substance when the fluid represents a liquid orsignifying matters such as dust particles, particulate maters orfragments of a substance when the fluid represents a gas.

BACKGROUND ART

Prevalently used conventional filter devices are classified by filteringmeans into those of a screen type provided with, for example, a metalscreen, a perforated panel or a slit panel, those of a cyclone type andthose of a centrifugal separation type, and are classified by cleaningsystem into those of a shaking system, those of a scraping system andthose of a backwash system.

The most serious problem in the conventional filter devices is a methodof discharging foreign matters deposited on the screen to prevent theclogging of the screen with foreign matters. Although various filterdevices of a shaking system, a scraping system and a backwash systemhave been proposed, those prior art filter devices need a dischargemeans of a large scale greater than that of their screening devices andrequire a high manufacturing cost, and the cleaning systems of thoseprior art filter devices are short of a perfect cleaning means.

It is an object of the present invention to provide a high-performance,economically advantageous filter device of a simple, rationalconstruction, capable of drastically solving technical problems residingin the prior art, easy to design and manufacture, capable of easilyremoving foreign matters deposited on a screen and discharging theforeign matters removed from the screen by either manual operation orautomatic operation using actuators, and capable of being constructed ina large scale without entailing any problem.

DISCLOSURE OF THE INVENTION

With the foregoing object in view, the present invention provides aself-gush-cleaning filter device comprising, as principal components, afilter casing provided with an inlet passage and an outlet passage, ascreen disposed within the filter casing so as to slide along the innersurface of the filter casing in the flowing direction of a fluid, aforeign matter ejecting opening formed between the screen and the inletpassage, a drive shaft for driving the screen, a screen driving unit fordriving the drive shaft so as to move the screen quickly in a downstreamdirection in which the fluid flows from the inlet passage toward theoutlet passage and to move the same slowly in an upstream directionopposite the downstream direction, and an outlet shutoff valve disposedin the outlet passage of the filter casing.

When removing foreign matters deposited on the screen from thisself-gush-cleaning filter device of the present invention, the outletshutoff valve is closed to disconnect the screen from a downstreampassage to form a closed chamber filled up with the fluid between thescreen and the outlet shutoff valve. Then, the screen driving unit isactuated to move the screen slowly in the upstream direction and to movethe screen quickly in the downstream direction. The fluid flows throughthe screen into the closed chamber from the upstream side of the screentoward the downstream side of the same while the screen is being movedgradually in the upstream direction. When the screen is moved quickly inthe downstream direction, the fluid contained in the closed chambergushes suddenly from the downstream side of the screen through thescreen into the upstream side of the same, so that foreign mattersdeposited on a surface of the screen on the upstream side are blown offthe screen by the force of the gushing fluid. The foreign matterejecting opening is opened to take out the foreign matters thus removedfrom the screen.

The screen driving unit may comprise a wiper cam mechanism for pushingthe drive shaft in the upstream direction, and a biasing member forbiasing the drive shaft in the downstream direction.

The screen driving unit may comprise a wiper cam mechanism for pushingthe drive shaft in the upstream direction, a piston mounted on the driveshaft, and a cylinder hermetically receiving the piston therein, andhaving a chamber for pushing the drive shaft in the downstream directioncommunicating with the inlet passage, and a chamber for pushing thedrive shaft in the upstream direction communicating with the atmosphere.

The screen driving unit may comprise a biasing member for biasing thedrive shaft in the upstream direction, a piston mounted on the driveshaft, and a cylinder loosely receiving the piston therein, and having achamber for pushing the drive shaft in the downstream direction,communicating with a space on the downstream side of an inlet shutoffvalve disposed in the inlet passage, and a chamber for pushing the driveshaft in the upstream direction, communicating with a space on thedownstream side of the outlet shutoff valve.

A scraping member may be disposed in sliding contact with a surface ofthe screen on the upstream side or the downstream side of the screen, orscraping members may be disposed in sliding contact with surfaces of thescreen on the upstream side and the downstream side of the screen,respectively.

Any or all of the screen driving unit, the outlet shutoff valve, theinlet shutoff valve and the foreign matter ejecting opening may beoperated automatically by an actuator or actuators.

The automatic operations of the actuators may be started on the basis ofa positional signal representing a position of the screen or on thebasis of a differential pressure signal representing a differentialpressure between the upstream side of the screen and the downstream sideof the same, and may be carried out in predetermined sequence.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of a self-gush-cleaning filterdevice in a first embodiment according to the present invention in astate where a screen has been moved to a limit downstream position;

FIG. 2 is a longitudinal sectional view of a self-gush-cleaning filterdevice in a second embodiment according to the present invention in astate where a screen has been moved to a limit downstream position;

FIG. 3 is a longitudinal sectional view of a self-gush-cleaning filterdevice in a third embodiment according to the present invention in astate where a screen has been moved to a limit downstream position;

FIG. 4 is a longitudinal sectional view of a self-gush-cleaning filterdevice in a fourth embodiment according to the present invention in astate where a screen has been moved to a limit downstream position; and

FIG. 5 is a longitudinal sectional view partly in a front view of aself-gush-cleaning filter device in a fifth embodiment according to thepresent invention in a state where a screen has been moved to a limitdownstream position.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will be describedhereafter with reference to the accompanying drawings.

Referring to FIG. 1 showing a self-gush-cleaning filter device in afirst embodiment according to the present invention, a filter casing 1is constructed by placing an inlet shutoff valve 13 in an inlet passagea formed in a filter body 1a provided with a foreign matter ejectingopening 15, placing an outlet shutoff valve 14 in an outlet passage dformed in the filter body 1a and putting a lid 1b on the filter body 1a.A cylindrical partition member 2 opening into the inlet passage a andthe outlet passage d is fitted in a vertical attitude within the filtercasing 1. A screen 11 is fitted in the partition member 2 so as to bevertically movable along the inner circumference of the partition member2. The screen 11 has a central portion fastened to a drive shaft 4 fordriving the screen 11, supported in bearings 9 and 10, and hermeticallyextending through a sealing member 9s fitted in the lid 1b. The driveshaft 4 is connected to a screen driving unit 3.

The screen driving unit 3 moves the screen 11 quickly in a downstreamdirection, i.e., the flowing direction of a fluid flowing from the inletpassage a toward the outlet passage d and moves the same slowly in anupstream direction, i.e., a direction opposite the flowing direction ofthe fluid. The screen driving unit 3 comprises a biasing member 6, suchas a coil spring, continuously biasing the drive shaft 4 in thedownstream direction, and a wiper cam mechanism combined with the driveshaft 4. When a handle included in this wiper cam mechanism is turned byhand, a wiper cam 5 is driven for turning by a torque applied theretothrough a reduction mechanism, and the wiper cam 5 pushes the driveshaft 4 axially in the upstream direction. The wiper cam 5 has a shaperesembling, for example, a scroll.

In a state where the outlet shutoff valve 14 has been closed, the driveshaft 4 is continuously biased in the downstream direction by thebiasing member 6. When the handle is turned to turn the wiper cam 5clockwise as viewed in FIG. 1, the wiper cam 5 pushes the drive shaft 4gradually in the upstream direction against the biasing force of thebiasing member 6. Upon the passage of the nose of the wiper cam 5 pastthe drive shaft 4, the lift of the wiper cam 5 changes suddenly from amaximum lift to a minimum lift, so that the drive shaft 4 is movedquickly in the downstream direction.

The operation of the self-gush-cleaning filter device thus constructedwill be described below.

The fluid is filtered as the same flows from the inlet passage a throughpassages b and c toward the outlet passage d and foreign mattersseparated from the fluid deposits on the upstream surface of the screen11. When ejecting the foreign matter deposited on the screen 11, theoutlet shutoff valve 14 is closed first to disconnect theself-gush-cleaning filter device from a downstream passage connectedthereto. Consequently, a closed chamber filled up with the fluid isformed between the screen 11, i.e., a wall having a moderate sealingproperty, and the outlet shutoff valve 14, i.e., a wall having a strictsealing property. The inlet shutoff valve 13 may be either opened orclosed.

Then, the screen driving unit 3 is operated to move the screen 11 slowlyin the upstream direction and to move the same quickly in the downstreamdirection. While the screen 11 is being moved slowly in the upstreamdirection and the volume of the closed chamber is gradually increasing,the fluid flows from the upstream side of the screen 11 through thescreen 11 into the closed chamber on the downstream side of the screen11. When the moving direction of the screen 11 is changed thereafter,the screen 11 moves quickly in the downstream direction. Consequently,the fluid gushes from the closed chamber on the downstream side of thescreen 11 through the screen 11 into the space on the upstream side ofthe screen 11, and the foreign matters deposited on the upstream surfaceof the screen 11 are blown off the screen 11 by the force of the gushingfluid.

This screen driving cycle, in which the screen 11 is moved slowly in theupstream direction and then moved quickly in the downstream direction,may be appropriately repeated. If scraping members, not shown, such asbrushes, are placed in sliding contact with the surface/surfaces of thescreen 11 on the upstream and/or the downstream side, the scrapingmembers are operated to promote the foreign matter removing action ofthe gushing fluid. The scraping member in sliding contact with thesurface of the screen 11 on the upstream side scrapes the foreignmatters off the screen 11 and the scraping member in sliding contactwith the surface of the screen 11 on the downstream side pushes theforeign matters through the meshes of the screen 11 toward the upstreamside.

The foreign matter ejecting opening 15 is opened at suitable times toeject the foreign matters thus separated from the surface of the screen11 on the upstream side and deposited on the bottom of the filtercasing 1. If the inlet shutoff valve 13 is kept closed during theejection of the foreign matters, the foreign matters are ejectedtogether with a volume of the fluid equal to that of a space between theinlet shutoff valve 13 and the outlet shutoff valve 14. If the inletshutoff valve 13 is kept open during the ejection of the foreignmatters, the foreign matters are flushed away by the fluid that flowsinto the self-gush-cleaning filter device at the pressure of the inletpassage a. Naturally, the force of the fluid which flushes away theforeign matters can be adjusted by adjusting the opening of the inletshutoff valve 13.

The foreign matter ejecting opening 15 is closed and the inlet shutoffvalve 13 and the outlet shutoff valve 14 are opened after the completionof the ejection of the foreign matters to return the self-gush-cleaningfilter device to its filtering work.

Thus, the present invention solves drastically and economically theforegoing problems which could not have been solved by the prior art.

FIG. 2 shows a self-gush-cleaning filter device in a second embodimentaccording to the present invention. The self-gush-cleaning filter devicein the second embodiment is obtained by replacing the biasing member 6biasing the drive shaft 4 in the downstream direction of the screendriving unit 3 employed in the first embodiment with a cylinder actuatorcomprising a piston 7 and a cylinder 8. A screen driving unit 3 employedin the second embodiment comprises a wiper cam mechanism, the piston 7mounted on a drive shaft 4 for driving a screen 11, the cylinder 8 inwhich the piston 7 is fitted, and a sealing member 7s disposed forsealing between the piston 7 and the cylinder 8. The wiper cam mechanismis similar to that employed in the first embodiment, and hence thedescription thereof will be omitted. The piston 7 divides the innerspace of the cylinder 8 into a chamber 8m and a chamber 8n. The chamber8m, which is used for moving the drive shaft 4 in the downstreamdirection, is connected to an inlet passage a by a connecting passage16, and the chamber 8n, which is used for moving the drive shaft 4 inthe upstream direction, is opened into the atmosphere. The pressure inthe chamber 8m, i.e., the pressure of the fluid in the inlet passage a,always exceeding the pressure in the chamber 8n, i.e., the atmosphericpressure, biases the drive shaft 4 always in the downstream direction,so that the same function of the biasing member 6 shown in FIG. 1 isobtained. Other particulars of the operating mode of theself-gush-cleaning filter device are the same as those of the operatingmode of the self-gush-cleaning filter device shown in FIG. 1 and hencethe description thereof will be omitted.

The chamber 8n may be connected to a negative pressure source, notshown, instead of being opened into the atmosphere to enhance thebiasing effect.

FIG. 3 shows a self-gush-cleaning filter device in a third embodimentaccording to the present invention. This self-gush-cleaning filterdevice is not provided with any mechanism corresponding to the wiper cammechanism for biasing the drive shaft 4 in the upstream directionincluded in the screen driving unit 3 of the self-gush-cleaning filterdevice in the first embodiment shown in FIG. 1, but theself-gush-cleaning filter device is provided with a biasing member 6 forbiasing a drive shaft 4 for driving a screen 11 in the upstreamdirection, and produces a high force for pushing the drive shaft 4 inthe downstream direction in a cylinder 8. A piston 7 is mounted on thedrive shaft 4 and fitted loosely in the cylinder 8. A chamber 8m towhich a pressure is applied to push the drive shaft 4 in the downstreamdirection is connected via a connecting passage 16 to a passagedownstream of an inlet shutoff valve 13, and a chamber 8n to which apressure is applied to push the drive shaft 4 in the upstream directionis connected via a connecting passage 17 to a passage downstream of anoutlet shutoff valve 14.

When removing foreign matters from the screen 11, the outlet shutoffvalve 14 is closed so that the pressure in the outlet passage dextending downstream from the outlet shutoff valve 14 prevails in thechamber 8n, and then the inlet shutoff valve 13 is closed and openedalternately to drive the screen 11. When the inlet shutoff valve 13 isclosed, the chamber 8m is disconnected from the inlet passage a throughwhich a pressure is applied to the chamber 8m, so that the piston 7under the biasing force of the biasing member 6 is moved slowly in theupstream direction as the fluid in the chamber 8m is allowed to flowthrough a small gap between the piston 7 and the cylinder 8. Finally thepressure working in the chamber 8m is balanced with that working in thechamber 8n and the screen 11 is held at a limit upstream position. Whenthe inlet shutoff valve 13 is opened thereafter, the pressure working inthe chamber 8m increases instantly to the pressure working in the inletpassage a, and the drive shaft 4 is pushed quickly in the downstreamdirection against the composite force of the pressure working in thechamber 8n and the biasing force of the biasing member 6. Thus, a screendriving function similar to that of the screen driving unit shown inFIG. 1 can be exercised. Other particulars of the operating mode of theself-gush-cleaning filter device are the same as those of the operatingmode of the self-gush-cleaning filter device shown in FIG. 1 and hencethe description thereof will be omitted.

In the embodiment shown in FIG. 3, it is desirable to place a smallstrainer 19 in the connecting passage 16 because a small amount of thefluid leaks from the inlet passage a through the connecting passages 16and 17 into the outlet passage d.

An example of scraping members 18a and 18b for scraping foreign mattersoff the screen 11 is shown in FIG. 3. The drive shaft 4 has a threadedportion provided with a thread of a great pitch and screwed in a bearing9. When the drive shaft 4 is moved axially by the operating force of thescreen driving unit 3, the drive shaft 4 rotates together with thescreen 11 fastened to the drive shaft 4. The scraping members 18a and18b are rotatably fitted on the drive shaft 4 so as to be able to rotaterelative to the drive shaft 4. Further, the scraping members 18a and 18bare disposed in sliding contact with the surfaces of the screen 11 onthe upstream and the downstream side, respectively, and are restrainedfrom turning relative to a filter casing 1. The scraping members 18a and18b move axially together with the screen 11. The shape, such as a shaperesembling a plate, a shape resembling teeth or a shape resembling abrush, of the scraping members 18a and 18b are dependent on the type ofthe screen 11, such as a mesh type, a porous type or slit type. Thescraping member 18a in contact with the upstream surface of the screen11, i.e., the surface on which foreign matters deposit, scrapes theforeign matters off the screen 11, and the scraping member 18b incontact with the downstream surface of the screen 11, i.e., the surfaceopposite the surface on which foreign matters deposit, pushes foreignmatters through the screen 11 toward the upstream side of the screen 11.The scraping members 18a and 18b may be provided with blades forconverting the flow of the fluid into a torque which rotates thescraping members 18a and 18b in sliding contact with the screen 11. Ifonly the cylindrical side wall of the screen 11 needs cleaning, scrapingmembers, not shown, fixedly placed in the filter casing 1 may beemployed.

FIG. 4 shows a self-gush-cleaning filter device designed for use at afluid inlet. The construction of this self-gush-cleaning filter deviceis similar to that of the self-gush-cleaning filter device shown inFIG. 1. As shown in FIG. 4, this self-gush-cleaning filter device is notprovided with any valve corresponding to the inlet shutoff valve 13, andis provided with an inlet passage b extending upstream of a screen 11and serving also as a foreign matter ejecting opening.

The movable components of the foregoing self-gush-cleaning filterdevices of the present invention, such as the screen driving unit 3, theinlet shutoff valve 13, the outlet shutoff valve 14 and a cover closingthe foreign matter ejecting opening 15, may be automatically operated byactuators. The operations of those actuators may be controlled in anautomatic sequential control mode, i.e., an unmanned control mode tocarry out automatically a series of operations including a foreignmatter removing operation, a foreign matter ejecting operation and afiltering condition setting operation.

FIG. 5 shows a self-gush-cleaning filter device in a fifth embodimentaccording to the present invention, capable of being operated in anunmanned control mode. The self-gush-cleaning filter device is providedwith a differential pressure measuring device 20 capable of measuringthe differential pressure between the opposite sides of a screen 11resulting from the resistance of foreign matters deposited on the screen11 against the flow of a fluid or a position transducing device, notshown, capable of sensing the variation of the position of the screen 11on the basis of the differential pressure. The differential pressuremeasuring device 20 and the position transducing device may bewell-known ones and hence the description thereof will be omitted. Theself-gush-cleaning filter device exercises a sequential control functionto operate sequentially actuators 5d, 14d and 15d for operating a screendriving unit 3, an outlet shutoff valve 14 and a foreign matter ejectingopening 15 to achieve an automatic sequential control operation.

An automatic sequential control comprises, by way of example, closingthe outlet shutoff valve 14 to disconnect a passage downstream of thescreen 11 when a differential pressure signal indicates the depositionof an excessive amount of foreign matters on the screen 11, actuatingthe screen driving unit 3 to blow the foreign matters deposited on theupstream surface of the screen 11 off the screen 11 by the force of thegushing fluid by moving the screen slowly in the upstream direction andmoving the same quickly in the downstream direction, and opening theforeign matter ejecting opening 15 to eject the foreign matters removedfrom the screen 11 (an inlet shutoff valve 13 may be kept either open orclosed as mentioned above). Thereafter, the foreign matter ejectingopening 15 is closed, and the outlet shutoff valve 14 is opened to setthe self-gush-cleaning filter device for a filtering process.

Although the inlet shutoff valve 13 included in the fifth embodiment asillustrated in FIG. 5 is operated by manually operating a handle 13d,naturally, the inlet shutoff valve 13 may be automatically operated.

A case 6c for containing a biasing member 6 as shown in FIG. 5 is atelescopic structure consisting of two tubes one nested in the other andcapable of extending in a predetermined range. The sufficientlycompressed biasing member 6 is contained in the case 6c to facilitatethe installation, inspection and replacement of the biasing member 6.The self-gush-cleaning filter device shown in FIG. 5 is provided with aconnecting passage p to allow a gas, such as air, accumulated in anupper portion of a filter casing 1 included in the self-gush-cleaningfilter device to escape downstream. If a gas accumulates in an upperportion of the filter casing 1, it is possible, when theself-gush-cleaning filter device is used for filtering a liquid, thatthe screen driving unit 3 is unable to make the liquid gush outsatisfactorily. Therefore, the gas must be made to escape from thefilter casing 1. A differential pressure produced by slightly narrowinga passage by a partition member 2 is used to conduct the gas accumulatedin an upper portion of the filter casing 1 in the downstream direction.

As is apparent from the foregoing description, although theself-gush-cleaning filter devices of the present invention exerciseepoch-making effects, many changes and variations may be made in andconventional techniques may be incorporated into the foregoingself-gush-cleaning filter devices of the present invention to meetrequests for the practical operation of the self-gush-cleaning filterdevices.

For example, although the inlet shutoff valve 13 and the outlet shutoffvalve 14 in each of the embodiments illustrated in FIGS. 1 to 5 take theshape of a butterfly valve, the shutoff valves 13 and 14 may be valvesof any type, such as gate valves, globe valves, ball valves or liftvalves, provided that the shutoff valves 13 and 14 are able to shut offthe corresponding passages. The foreign matter ejecting opening 15 maybe provided with a valve of any suitable type.

Naturally, the biasing member 6 may be any suitable member other than anelastic member, such as shown in FIGS. 1, 3, 4 and 5, such as acombination of a weight and a linkage, a power-assisted biasing member,a pneumatic biasing device or a hydraulic biasing device.

Naturally, the self-gush-cleaning filter device of the present inventionmay be provided with either only a single screen as shown in FIG. 3 or aplurality of screens. Each of the self-gush-cleaning filter devices ofthe present invention shown in FIGS. 1, 2, 4 and 5 is provided with thescreen 11 of a relatively fine mesh, and a screen 12 of a relativelycoarse mesh disposed on the upstream side of the screen 11. Foreignmatters removed from the fine screen 11 by the action of the gushingfluid drop by gravity, pass the coarse screen 12, and collect togetherwith coarse foreign matters removed from the coarse screen 12 on thebottom of the filter casing 1. The coarse screen 12 may be fixedlydisposed in the filter casing 1 as shown in FIGS. 1, 2, 4 and 5 or maybe mounted, similarly to the fine screen 11, on the drive shaft 4 so asto move together with the drive shaft 4.

The screens 11 and 12 may be made of any suitable material, such as ametal, a synthetic resin, synthetic fibers or the like. It is desirableto form the screens 11 and 12 of a somewhat elastic material because themeshes of a screen formed of somewhat elastic material are expanded bythe gushing fluid to facilitate the separation of foreign matters caughtin the meshes. The screens 11 and 12 may be formed of an inelasticmaterial. A suitable material for forming the screens 11 and 12 isdetermined selectively taking into consideration the necessary strengthand the screening performance of the screens.

It is desirable to form the bottom wall of the filter casing 1 so thatthe main passage extends apart from the foreign matters removed from thefilters 11 and 12 by the gushing fluid and deposited on the bottom ofthe filter casing 1 to prevent the foreign matters deposited on thebottom of the filter casing 1 from being raised by the flow of the fluidand to prevent the foreign matters from depositing again on the screens11 and 12. It is desirable to form the passage so that the fluidgenerally flows in a direction opposite the acting direction of gravity,i.e., upward. The partition member 2 may be formed integrally with thefilter body 11a if the material forming the filter body 1a permits.

If the foreign matters removed from the screens by the gushing fluidneed to be raised for ejection, the foreign matters may be carried by amechanical conveying method using buckets or a conveyor, by a pump or bythe flow and pressure of the fluid flowing through the inlet passage a.In case of using a fluid the ability of the fluid to raise the foreignmatters is dependent on conduit conditions including the flow rate andthe pressure of the fluid. If the conduit conditions permit, theself-gush-cleaning filter device of the present invention may beinstalled in an underground pit and the foreign matter ejecting openingand foreign matter discharge passages e through f may be installed onthe ground. If the flow rate and the pressure of the fluid areexcessively high, the force of the foreign matter discharge may beproperly suppressed by adjusting the opening of the inlet shutoff valve13.

The positional relation between the components of the self-gush-cleaningfilter device of the present invention and the like may be changedwithin the scope of the present invention, and the present invention isnot limited in its practical application to the foregoing embodiments.

INDUSTRIAL APPLICABILITY

As is apparent from the foregoing description, the present invention isbased on a new technical idea of removing foreign matters deposited on ascreen from the screen by the force of a gushing fluid caused to gushmainly by varying the volume of a closed space containing the fluid, theself-gush-cleaning filter device of the present invention has a simple,lucid construction and is capable of drastically solving the technicalproblems in cleaning the clogged screen of the prior art filter device.The self-gush-cleaning filter device of the present invention enablesthe easy removal of foreign matters from the screen and ejection of theremoved foreign matters by either a manual operation or an automaticoperation using actuators. The self-gush-cleaning filter device of thepresent invention can be constructed in a large scale without entailingany problem, is economically advantageous and is capable of exercisinghigh performance. Thus, the self-gush-cleaning filter device of thepresent invention provides advantages in design, manufacture andmaintenance control and have a great effect as compared with that of theprior art.

What is claimed is:
 1. A self-gush-cleaning filter device comprising:a filter casing provided with an inlet passage and an outlet passage; a screen disposed within the filter casing so as to slide along an inner surface of the filter casing in a direction of flow of a fluid; a foreign matter ejecting opening means formed between the screen and the inlet passage; a drive shaft for driving the screen; a screen driving unit for driving the drive shaft so as to move the screen quickly in a downstream direction in which the fluid flows from the inlet passage toward the outlet passage and to move the screen slowly in an upstream direction opposite the downstream direction; and an outlet shutoff valve disposed in said outlet passage; wherein said screen driving unit comprises: a wiper cam mechanism for pushing the drive shaft in the upstream direction; a piston mounted on the drive shaft; and a cylinder hermetically receiving the piston therein and having a first chamber communicating with the inlet passage, for pushing the drive shaft in the downstream direction, and a second chamber located opposite said first chamber and communicating with the atmosphere.
 2. A self-gush-cleaning filter device comprising a filter casing provided with an inlet passage and an outlet passage;a screen disposed within the filter casing so as to slide within an inner surface of the filter casing in a direction of flow of a fluid; a foreign matter ejecting opening means formed between the screen and the inlet passage; a drive shaft for driving the screen; a screen driving unit for driving the drive shaft so as to move the screen quickly in a downstream direction in which the fluid flows from the inlet passage toward the outlet passage and to move the screen slowly in an upstream direction opposite the downstream direction; and an outlet shutoff valve disposed in said outlet passage; wherein said inlet passage has an inlet shutoff valve therein; and said screen driving unit comprises: a coil spring coaxially mounted around said drive shaft and exerting a constant biasing force to constantly bias the drive shaft in the upstream direction; a piston mounted on the drive shaft; and a cylinder slidably receiving the piston therein and having a first chamber communicating with a space on a downstream side of the inlet shutoff valve, for pushing the drive shaft in the downstream direction, and a second chamber communicating with a space on a downstream side of the outlet shutoff valve, for pushing the drive shaft in the upstream direction; and wherein said screen has an upstream side surface and a downstream side surface, and a scraping member is disposed in sliding contact with at least one of the upstream and downstream side surfaces of the screen.
 3. The self-gush-cleaning filter device according to claim 1, wherein said screen has an upstream side surface and a downstream side surface, and a scraping member is disposed in sliding contact with at least one of the upstream and downstream side surfaces of the screen.
 4. The self-gush-cleaning filter device according to claim 1, wherein at least one of the screen driving unit, the outlet shutoff valve and the foreign matter ejecting opening means has an actuator for automatic operation thereof.
 5. The self-gush-cleaning filter device according to claim 3, wherein at least one of the screen driving unit, the outlet shutoff valve and the foreign matter ejecting opening means has an actuator for automatic operation thereof.
 6. The self-gush-cleaning filter device according to claim 2, wherein at least one of the screen driving unit, the outlet shutoff valve, the inlet shutoff valve and the foreign matter ejecting opening means has an actuator for automatic operation thereof.
 7. The self-gush-cleaning filter device according to claim 4, further comprising means connected to said actuator for operating the actuator in response to a positional signal representing a position of the screen, to carry out an automatic operation in a predetermined sequence.
 8. The self-gush-cleaning filter device according to claim 4, further comprising means connected to said actuator for operating the actuator in response to a differential pressure signal representing a differential pressure between an upstream side of the screen and a downstream side of the screen, to carry out an automatic operation in a predetermined sequence.
 9. The self-gush-cleaning filter device according to claim 5, further comprising means connected to said actuator for operating the actuator in response to a positional signal representing a position of the screen, to carry out an automatic operation in a predetermined sequence.
 10. The self-gush-cleaning filter device according to claim 5, further comprising means connected to said actuator for operating the actuator in response to a differential pressure signal representing a differential pressure between the upstream side of the screen and the downstream side of the screen, to carry out an automatic operation in a predetermined sequence.
 11. The self-gush-cleaning filter device according to claim 6, further comprising means connected to said actuator for operating the actuator in response to a positional signal representing a position of the screen, to carry out an automatic operation in a predetermined sequence.
 12. The self-gush-cleaning filter device according to claim 6, further comprising means connected to said actuator for operating the actuator in response to a differential pressure signal representing a differential pressure between the upstream side of the screen and the downstream side of the screen, to carry out an automatic operation in a predetermined sequence. 